Tube forming apparatus



March 18, 1969 J O, L N

TUBE FORMING APPARATUS Sheet Filed Dec. 29. 1966 [NV/EN TOR. JOHN O. LENZ ATTORNEY March 18, 1969 O. LENZ TUBE FORMING APPARATUS Sheet of 2 Filed Dec. 29, 1966 IINVENTOR. JOHN o. LENZ ATTORNE 6 Claims Int. Cl. B21b 19/08, 22/00; B21d 3/06 ABSTRACT OF THE DISCLOSURE Apparatus for reducing the Wall thickness of tubing by spinning in which the workpiece is drawn between a mandrel and relatively rotating rollers by a ram driven axially through the center of the mandrel.

The blanks used in spin forming of thin wall tubing may be produced by punch press drawing, which is practical down to wall thicknesses obtainable with a few drawing operations. To attain further significant reduction in wall thickness it is more practical to work the tube on a mandrel with rollers that rotate around the tube as it is advanced axially. One arrangement for performing this spinning operation is described in the United States patent to Chirtis No. 2,522,257. In that patent the rollers are cylindrical with conical leading surfaces and are supported and turned by an outer race similar to that of a roller bearing. A cup-shaped blank is placed on a mandrel which is advanced through the rollers with attendant elongation and thinning of the tube wall. This mandrel must be at least as long as the finished tube.

The apparatus of the present invention may be considered an improvement of the Curtis structure and is particularly advantageous in forming tubes of considerable length. The difiiculty of making satisfactory mandrels increases geometrically as the size is increased. In larger sizes it becomes much more diificult to hold satisfactory tolerances in diameter and straightness if the tubes produced are to have the desired uniformity from end to end. The solution to this problem provided by the present invention is to pull the tube under the rollers and over a short length of mandrel. This short, Working surface of the mandrel can be made accurately cylindrical rather easily and since it remains under the rollers during the entire spinning operation, the tubes produced will be of uniform thickness throughout their lengths. According to the present invention a ram driven through the mandrel engages the inner surface of the bottom of the cup-shaped blank to move that end of the blank away from the working surface of the mandrel and draw the blank through the spinning rollers.

FIGURE 1 of the drawing is a sectional elevation showing the apparatus in loading position, FIGURE 2 shows the same apparatus during the spinning operation, and FIGURE 3 is a diagrammatic illustration of a spinning machine incorporating the mandrel arrangement of FIGURES 1 and 2.

A roller assembly 10 is carried in a member 12 which is adapted to be rotated about a horizontal axis as shown in the drawing. The roller assembly may be similar to that disclosed in the above-mentioned Curtis Patent No 2,522,257. A plurality of rollers 14 are arranged to roll on a cylindrical race 16. A retaining ring 18 is adapted to maintain the rollers in proper spaced relation, while the annular inner surface of a plate 20 serves to prevent axial displacement of the ring 18. Each roller has a cylindrical portion that rolls on race 16 and a frusto-conical portion adapted to reduce the diameter of the workpiece.

FIGURE 1 shows the apparatus in loading position with a relatively thick walled cup-shaped workpiece 24 situated on a cylindrical mandrel 26. The mandrel 26 is 10- nited States Patent 3,433,040 Patented Mar. 18, 1969 cated on the same axis as the roller assembly and is adapted to be advanced toward the roller assembly on that axis. The end portion 26a of the mandrel 26 is made of wear resistant material such as tungsten carbide and the extreme front end is curved to conform to the inner configuration of the workpiece. The front surface of the mandrel is formed by a member 28 which is separate from portion 26 and movable with respect thereto. In the position of FIGURE 1, the member 28 is retracted into the mandrel so that its outer surface continues the curved surface of the mandrel portion 26a which fits the inside of the workpiece. The member 28 is carried on the end of a rod 30 that is coaxial with the mandrel surface and movable axially with respect thereto. A ball bearing 32 is carried by the rod 30 and the member 28 is, in turn carried by the ball bearing so that the member 28 is free to rotate with respect to the mandrel during the spinning operation.

The mandrel 26 is carried by a piston 35 which is movable in a cylinder 37. The piston '35 has a head 35a guided by the cylinder wall and a reduced cylindrical portion 35b guided by an opening in an end plate 39 covering the lefthand end of cylinder 37. The rod 30 is slidable in an axial bore in the piston 35 and its righthand end carries a piston 42 which slides in the cylinder 37. A plate 44 closes the righthand end of the cylinder 37.

The cylinder '37 is connected to a hydraulic circuit by means of which the pistons 35 and 42 are moved to move the mandrel 26 and the member 28 with respect to the roller assembly 10.

As seen in FIGURE 3, the roller assembly 10 and the cylinder 37 are carried on a frame 50. Also mounted on frame 50 are a motor 5 2 which drives the roller assembly through a belt 54, and a motor 57 which drives a pump 59. The pump 59 is fed from an oil reservoir 61 by a pipe 63 and delivers oil through a pipe 65 to a four-way valve 67 which can be positioned to drive the pistons 35 and 42 in cylinder 37 either to the right or to the left. In the valve position shown, oil is delivered from the pump 59 through a pipe 69 to the righthand end of the cylinder 37, and oil is discharged from the lefthand end of the cylinder through the pipe 71, through a volume control valve 73 and a pipe 75 to the four-way valve 67 and thence to the reservoir 61.

The motors 52 and 57 are energized from a source of electric power through supply lines 78 and '80. A line switch 82 together with a limit switch 84 and a momen tary manual switch 86 control the supply of current to the motors. The limit switch 84 is normally closed so closure of line switch will turn the roller assembly and pump oil to cylinder 37.

With the workpiece 24 on the mandrel as shown in FIGURES 1 and 3, oil is admitted to the righthand end of cylinder 37, moving piston 42 to the left. Oil in the space between pistons 42 and 35 moves the mandrel 26 to the left at a rate determined by the volume control valve 73. The mandrel 26 together wth the member 28 will continue moving to the left until the piston head 35a is stopped by engaging the end plate 39. In this position of the mandrel 26 the hardened wear surface 26a lies within roller assembly 10 with the rollers 14 in position to reduce the wall thickness of the workpiece 24. The spinning operation up to this point is similar to that described in the aforementioned Curtis Patent No. 2,522,257.

When piston 35 reaches the limit of its movement to the left, a port 90 in the wall of cylinder 37 is exposed to permit oil to flow from between pistons 35 and 42 through a pipe 91 and check valve 93. Thus, piston 42 together with rod 30 and member 28 continue to move to the left, and while the work surface 26a of the mandrel 26 remains under the spinning rollers 14, the bottom of the cup-shaped workpiece 24 is moved to the left as illustrated in FIGURE 2. Such movement will continue with concurrent reduction in wall thickness of t workpiece until the bottom of the workpiece engages and actuates the limit switch 84 to open circuit position to stop both the roller assembly and the pump. The manual switch can be closed to run the workpiece entirely through the roller assembly, or the four-way valve 67 can be reversed and the mandrel 26 and member 28 backed out of the roller assembly.

As mentioned above, the ball bearing 32 carries the member 2-8 on the rod 30. It has been found that as the roller assembly rotates at relatively high speed with respect to the mandrel, the workpiece rotates at a rather low speed on the mandrel. The ball bearing permits the member 28 and the bottom of the cup-shaped workpiece to turn freely with respect to the rod 30. Thus, the free length of thin section tubing between the roller assembly and the member 28 is subjected only to tensile forces and distortion due to torque is avoided.

In order to return the mandrel 26 and member 28 to the position of FIGURE 1, the four-way valve 67 is rotated ninety degrees. In this valve position, oil from the pump will be delivered through pipe 75 and a check valve 76 to the pipe 71 to the lefthand end of cylinder 37, forcing pistons 35 and 42 to the right. A check valve 95 in piston head 3511 allows oil to refill the space between the pistons and return the mandrel to its loading position.

The embodiments of the invention in which an exclusive property or right is claimed are defined as follows:

1. Apparatus for reducing the wall thickness of a tube comprising, a mandrel having a cylindrical Work surface of an axial length less than the length of the finished tube, a plurality of rollers spaced radially from the axis of the mandrel by the radius of the finished outer surface of the tube, means for causing relative rotation of said mandrel and rollers, a member adapted to engage the tube beyond the end of the mandrel, and a shaft extending through said mandrel carrying said member and movable axially of said mandrel to move the tube axially of said mandrel and said rollers.

2. Apparatus as defined in claim 1 in which means is provided to move the mandrel axially between a position removed from the rollers and a position with the rollers over the work surface.

3. Apparatus as defined in claim 1 in which the tube engaging member is supported on the shaft by an antifriction bearing.

4. Apparatus for reducing the wall thickness of a tube having a closed end comprising, a mandrel having a cylindrical work surface of an axial length less than the length of the finished tube and adapted to support the tube, a plurality of rollers disposed generally in a plane normal to the mandrel axis adapted to cooperate with said mandrel in reducing the wall thickness of the tube, means for causing relative rotation of said mandrel and said rollers about the mandrel axis, a member adapted to engage the inner surface of the closed end of the tube, and a shaft extending through said mandrel engaging said member and movable axially to move the closed tube end with respect to said rollers and said mandrel.

5. Apparatus as defined in claim 4 in which the mandrel is relatively movable axially between a tube loading position remote from the rollers and a position with the plane of the rollers intersecting the Work surface.

6. Apparatus for reducing the wall thickness of a tube comprising, a mandrel having a cylindrical work surface of an axial length less than the length of the finished tube, a tool spaced radially from the axis of the mandrel by the radius of the finished outer surface of the tube, means for causing relative rotation of said mandrel and said tool, means for moving said mandrel between a loading position and a position cooperating with said tool, a member adapted to engage the tube beyond the end of the mandrel, a shaft extending through said mandrel carrying said member, and means to move said shaft axially of said mandrel and said tool as said manadrel and tool are relatively rotated.

References Cited UNITED STATES PATENTS 1,985,833 12/1934 Lampart 72-85 2,160,975 6/1939 Matter et al. 72-85 2,522,257 9/1950 Curtis 72-124 3,046,924 7/1962 Kane 7285 RICHARD J. HERBST, Primary Examiner.

US. Cl. X.R. 

